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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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    <script>
        // var cat = {
        //     name:"miaomiao",
        //     age:2
        // }

        // console.log(cat.name);  // . 的

        // var student = null;  //null什么都没有（空）

        var v;
        console.log(v);

    </script>
</body>
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